1. Field of the Invention
The present invention relates to a liquid crystal display device having an improved viewing angle, and more particularly, to a liquid crystal display device and a driving method thereof to prevent the degradation of image quality that may be generated from applying halftone gray.
2. Background of the Related Art
Generally, a liquid crystal display device is employed for displaying an image by supplying matrix-like arranged liquid crystal cells with data signals according to image information to adjust a light transmission of liquid crystal cells.
A liquid crystal display device consists of a liquid crystal display panel on which a plurality of liquid crystal cells forming a pixel unit are arranged in an active matrix form and a driver integrated circuit (IC) for driving the liquid crystal cells.
The liquid crystal display panel consists of a color filter substrate, a thin film transistor array substrate opposite the color filter substrate, and a liquid crystal layer inserted between the color filter and thin film transistor array substrates.
Common and pixel electrodes are formed on the two inner sides of the color filter and thin film transistor array substrates, respectively, to apply an electric field to the liquid crystal display panel. Each of the pixel electrodes is formed on the thin film transistor array substrate to match the corresponding liquid crystal cell, while the common electrode is formed in one body on an entire surface of the inner side of the color filter substrate. Hence, a light transmission of each of the liquid crystal cells can be individually adjusted by controlling a voltage applied to the corresponding pixel electrode while a voltage is applied to the common electrode.
A plurality of data lines are also formed on the thin film transistor array substrate of the liquid crystal display panel to transfer data signals supplied from a data driver integrated circuit to the liquid crystal cells. A plurality of gate lines that cross the data lines transfer scan signals supplied from a gate driver integrated circuit to the liquid crystal cells. And, the liquid crystal cells are defined by crossings between the data and gate lines.
The gate driver integrated circuit sequentially supplies a plurality of the gate lines with the scan signals, respectively to select each line of the matrix-like arranged liquid crystal cells sequentially. And, the liquid crystal cells of the selected line are provided with the data signal from the data driver integrated circuit.
Thus, in order to control the voltage applied to the pixel electrode by each liquid crystal cell, a thin film transistor is formed as a switching device in each of the liquid crystal cells, and a conductive channel is generated between source/drain electrodes of the thin film transistor in each of the liquid crystal cells when the scan signal is applied to a gate electrode of the corresponding thin film transistor through the corresponding gate line. In this case, the data signal applied to the source electrode of the thin film transistor through the data line, via the drain electrode of the thin film transistor, to be applied to the corresponding pixel electrode, whereby the light transmission of the corresponding liquid crystal cell is controlled.
The above-explained liquid crystal display device is explained by referring to the attached drawings as follows.
FIG. 1 illustrates a schematic layout of a liquid crystal display panel prepared by bonding a thin film transistor array and a color filter substrate to each other.
In FIG. 1, a liquid crystal display panel 10 includes an image display unit 13 on which a plurality of liquid crystal cells are arranged like a matrix form, a gate pad unit 14 to which gate lines of the image display unit 13 are connected, and a data pad unit 15 connected to data lines thereof. The gate and data pad units 14 and 15 are formed on a peripheral area of a thin film transistor array substrate 11 which is not overlapped with a color filter substrate 12. The gate pad unit 14 supplies the gate lines of the image display unit 13 with scan signals supplied from a gate driver integrated circuit, and the data pad unit 15 supplies the data lines of the image display unit 13 with image information supplied from a data driver integrated circuit.
Although not shown in the drawing specifically, on the thin film transistor array substrate 11 of the image display unit 13, the data lines to which the image information is applied and the gate lines to which the scan signals are applied are arranged to cross each other.
Moreover, on the thin film transistor array substrate 11 of the image display unit 13, pixel electrodes are connected to the corresponding thin film transistors to drive the liquid crystal cells, and a passivation layer is on an entire surface to protect the electrodes and thin film transistors.
Color filters, on the color filter substrate 12 of the image display unit 13, are coated and separated by a black matrix into cell units and a common transparent electrode as a counter electrode against the pixel electrodes on the thin film transistor array substrate 11.
The above-constructed thin film transistor array and color filter substrates 11 and 12 are separated by a spacer to provide a cell gap. The cell gap is filled with liquid crystals.
Then, the thin film transistor array and color filter substrates 11 and 12 are bonded to each other by a sealing unit 16 formed on a periphery of the image display unit 13.
However, the above-explained liquid crystal display device has a small viewing angle and a brightness relatively poorer than that of other display devices. Hence, many efforts have been made to improve the viewing angle and light transmission in LCD field.